What do anonymous people gender you as you're just going about your life? And how do they treat you?
Once you start really getting out there and just living your life and actually interacting with the world, it should become apparent very quickly whether you pass or not. Hang out with female friends, go shopping, go to restaurants, and see if you hear people calling you "ladies." See if cashiers and bank tellers and the like call you "miss/ma'am." Listen for diminutive nicknames like "honey," "sweetheart," etc. And listen for gender-specific pronouns in conversations... if people call you "she" or "he." (Another thing that happens sometimes is that if someone isn't sure what your gender is, or if people's perceptions seem to be mixed, you often can hear people deliberately avoiding pronouns, using gender-non-specific language. It's uncommon, but it happens too.)
Also, pay attention to how people greet you. When I was first considering going full-time, and tended to be getting gendered both male and female depending on the perception of the person, just the speaking tone and body language of other people was a good indicator of whether they were gendering me male or female. When people are perceiving you as male, there's a sort of "repsect" that you'll get, kind of a "yes, you are a dominant male, I'm respecting your authority and your personal space and not getting too emotionally-connected with you" sort of attitude. Where women are greeted much more openly, with more pitch variation and inflection in the voice. And you'll be able to see guys doing this sort of "talking down to you" attitude, and women doing this sort of "openly greeting you like a friend" attitude. You can look for that.
This is all about just judging how other people are perceiving you, gauging their reactions.
Stares are honestly a bad way to do it. Because we tend to associate stares with "OMG that is a man in a dress, look at the freak," when in reality it could mean that people find you attractive, or are studying a unique body feature, or a unique appearance, or find your hairstyle interesting, or find your clothes interesting, or at worst are trying to figure out whether you're male or female because they aren't sure upon first glance. Tall cis girls get stared at all the time, as do very short people, as do people with a unique sense of style, as do beautiful people, as do ugly people, as do people with any sort of disability or any sort of feature that looks unique. People are curious. It doesn't mean they're misgendering you or judging you.